Close-up filter is a simple secondary lens used to enable macro photography without requiring a specialized primary lens. They work identically to reading glasses, allowing any primary lens to focus more closely.

Close-up lenses typically mount on the filter thread of the primary lens, and are manufactured and sold by suppliers of photographic filters.

While some single-element close-up lenses produce images with severe aberrations, there are also high-quality close-up lenses composed as achromatic doublet which are capable of producing excellent images, with pretty low loss of sharpness.